( 75 ) 



Physics. — Communication N" 94^ I tiiid II fVom the physical 

 laboratory at Leiden by Prof. H. Kamerlingh Onnes. 



(Communicated in the meeting of May 27, 1905). 



I. Improvement to the open mercury manometer of reduced heüjht 

 with transference of pressure by means of compressed gas. 



In Comm. N° 44, Oct. '98, § 6, is described how the steel capillary 

 tubes q were cemented on to the glass tubes m (see figs. 1 and 4 

 of the plate belonging to Comm. N" 44, of which the part that has 

 been modified is reproduced here as fig. 2 of the annexed plate). It 

 was also remarked that from time to time these connections became 

 defective (tliey slipped otF when soft cement was used, or leaked 

 when hard cement was used), and that therefore we were trying to 

 find a better method of connecting. Since that time we have succeeded 

 in finding a way to make perfectly trustworthy joints. For the useful- 

 ness of the manometer this is of great importance. 



Fig. 1 shows the connection as made now. It is based on the 

 method of Cailletet to solder glass on to metal, which method has 

 been mentioned in Comm. N" 27, II, June '96, for similar purposes 

 and as appears from Comms. N" 85, .June '03, and N" 89, Nov. '03, 

 has stood the proof in several cases where it was applied. The steel 

 capillary q^^ reaches as high as q^^ in the glass tube h^, which has 

 a wider part h^^, containing mercury which is separated from the 

 junctures of b^^ and p^ by a layer of marine glue b^^ in b-^^. Fol- 

 lowing the above mentioned method, the end of b^^ has been plati- 

 nised, then coppered galvanically and soldered on to p^. 



This connection has quite answered the expectations. With the 

 former method when the manometer was put under pressure it some- 

 times appeared that minute cracks had come in the sealing wax, 

 through which the compressed gas which transfers the pressure from 

 one manometer column to the other escaped. In case it escaped 

 rapidly, the mercury of one manometer tube flew into the other 

 before the pressure could be removed and within a few moments 

 the apparatus was defect and wanted a thorough rearrangement to 

 become again fit for use. This has never occurred with the new 

 connections, and yet they have been used for a long time. If a tiny 

 opening should have remained in the marine glue, the mercury has 

 first to pass through it and a mercury drop at y; gives warning. Then 

 the manometer can be freed in time from pressure and when the leak 

 of the single tube is repaired it may be immediately used again. 



6 



Proceedings Royal Acad. Amsterdam. Vol. Vill. 



